Two people have died so far due to a listeria outbreak in the U.S., the Centers for Disease Control and Prevention (CDC) alerted on Friday.

Listeria is the third-leading cause of death from foodborne illness in the country, according to the health agency.

Twenty-eight people across 12 states have reported illness from listeria infection — with New York and Maryland reporting the highest number of cases.

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The first illness was reported on May 29, and the most recent was on July 5, per CDC data.

The two deaths occurred in Illinois and New Jersey.

Deli meat - listeria

Two people have died so far due to a listeria outbreak in the U.S., the Centers for Disease Control and Prevention alerted on Friday. (iStock)

In many cases, the bacterial outbreak has been linked to people eating sliced meats purchased at deli counters, the CDC stated.

The bacteria is known to spread easily in delis and in environments where food is prepared.

No specific brands have been identified as of yet — and the CDC noted that officials are investigating.

Symptoms of listeria

The most common symptoms of infection include fever, fatigue and muscle aches. 

Some people also experience stiff neck, headache, balance problems, seizures or disorientation, according to the CDC.

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These symptoms are typically reported within two weeks of consuming contaminated food, but could appear before or after that time frame.

Who is at highest risk?

"In general, the risk is low, but certain populations are at higher risk for severe disease," Dr. Paul Sax, MD, clinical director of the Division of Infectious Diseases at Brigham and Women’s Hospital in Boston, told Fox News Digital via email.

Those who are pregnant, are 65 years of age or older or have a weakened immune system are most vulnerable to listeria, the CDC warned. 

"This is because listeria is more likely to spread beyond their gut to other parts of their body, resulting in a severe condition known as invasive listeriosis," the agency stated in the alert.

Pregnant nauseous woman

Pregnant women infected with listeria could potentially experience premature birth, miscarriage or stillbirth, the CDC warned. (iStock)

Pregnant women infected with listeria could potentially experience premature birth, miscarriage or stillbirth.

"Pregnant women are counseled to avoid eating soft cheeses and delicatessen meats for this reason," Sax warned.

It is also possible for the infection to be passed along to the baby, which can be life-threatening.

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"Other people with invasive illness – most commonly adults 65 years and older and people with weakened immune systems – usually have infection of the bloodstream (sepsis) or brain (meningitis or encephalitis)," the CDC states.

For most people outside these high-risk groups, the infection is not likely to cause serious illness.

Preventing and treating infection

For those at higher risk, the CDC recommends avoiding eating sliced deli meats unless they are reheated to an internal temperature of 165°F, then cooled before eating.

Refrigeration does not kill the bacteria, the agency noted.

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The CDC also recommends cleaning all containers and surfaces that may have come into contact with sliced deli meats.

"During a reported outbreak, people should discard any of the foods associated with this outbreak pending further notice," Sax advised. 

Deli counter

In many cases, the bacterial outbreak has been linked to people eating sliced meats purchased at deli counters, the CDC stated. (iStock)

"Over the years, there have been multiple such events, including things like ice cream, cantaloupes, hard boiled eggs and salad greens," he added.

Anyone who experiences listeria symptoms should contact a health care provider immediately, health officials say. 

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"The standard of care treatment is ampicillin (a common antibiotic), given at high doses intravenously," Sax said.

Fox News Digital has reached out to medical experts for comment.